Relationship between serum leptin and the insulin-like growth factor-I system in humans

The growth hormone (GH)/insulin-like growth factor-I (IGF-I) system and lep tin both play an important role in the regulation of body composition. Alth ough the regulation of these two hormonal systems by insulin has been under intense investigation, the physiologic interactions between leptin and the GH/IGF-I system remain unknown. In this study, we examined the relationshi ps among circulating leptin and key elements of the IGF-I system in 60 subj ects (27 nondiabetic lean, 21 nondiabetic obese, and 12 type 1 diabetic sub jects) with a wide range of insulin secretory capacity. Leptin, glucose, in sulin, free IGF-I, total IGF-I, IGF-binding protein-1 (IGFBP-1), and IGFBP- 3 levels were measured in the basal state after an overnight fast, and the acute insulin response to glucose (AIRG) was determined after intravenous g lucose injection. AIRG was significantly higher (P <.01) in the obese (3,36 5 +/- 562 pmol/L . min) versus lean subjects (1,624 +/- 155 pmol/L min). In simple regression analysis, the serum leptin concentration was positively correlated with the body mass index ([BMI] men, r=.51, P=.005; women, r=.71 , P<.001), IGFBP-3 (men, r=.20, P= nonsignificant; women, r=.41, P<.025), a nd AIRG (men, r=.73, P <.001;women, r =.62, P <.01). There was a nonlinear correlation between leptin and IGFBP-1,but there was no correlation between leptin and free or total IGF-I. In multiple regression analysis with lepti n as the dependent variable, gender, BMI, and IGFBP-3 entered the equations at a statistically significant level. The correlation of leptin with IGFBP -3 was independent of obesity and persisted after correction for AIRG, sugg esting a link between leptin and GH action. Copyright (C) 1999 by W.B. Saun ders Company.